A microwave quantum frequency comb system

Abstract

The application provides a microwave quantum frequency comb system, comprising at least three Josephson junction arrays, wherein one end of a first Josephson junction array is inputted with a microwave signal or a high-speed pulse signal, and the first Josephson junction array is connected to other multiple Josephson junction arrays through filtering modules respectively at two ends of branch leads with selectable numbers of Josephson junctions on the other multiple Josephson junction arrays, so as to output voltage signals to a specific number of Josephson junctions of the other multiple Josephson junction arrays, and then the other multiple Josephson junction arrays output variable frequency microwave signals at two ends respectively, and the microwave signals outputted at two ends of the above multiple Josephson junction arrays are combined and outputted through a combiner, so that the microwave signal with a comb-shaped distribution of multiple frequency components can be realized, and the frequency of each component can be changed through real-time control switching of corresponding Josephson junction array leads by opening and closing of an external circuit program.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated superconducting Josephson junction array circuit design, and particularly relates to a microwave quantum frequency comb system. BACKGROUND

[0002] The frequency comb system is a special signal source capable of emitting multiple spectral lines, and is widely used in precise testing fields such as optical clocks, laser radars and spectroscopy. The on-chip frequency comb system has made a breakthrough in the field of optics, but the on-chip frequency comb in the microwave band is rarely reported. In particular, in some low-temperature application scenarios, such as quantum computing and other heat loads, the on-chip frequency comb in the microwave band begins to be valued.

[0003] The microwave source based on the superconducting Josephson junction has an innate advantage for the above-mentioned low-temperature application, and has very low power dissipation. The reported on-chip frequency comb in the microwave band is based on the alternating current Josephson effect, that is, when a direct current voltage is loaded on both ends of the Josephson junction, an alternating current signal will be radiated on both ends of the Josephson junction, and the frequency of the signal is directly determined by the voltage. According to the Josephson formula: f = V dc ·(2e / h). Wherein, e is the electronic charge, V dc is the direct current voltage loaded on both ends of the Josephson junction, and h is the Planck constant. The signal resonance is realized by embedding the Josephson junction in a microwave resonant cavity with extremely high quality parameters. The microwave signal generated thereby is a series of equally spaced spectral lines in the frequency spectrum, and a series of highly coherent microwave signals in the time domain. This microwave frequency comb structure is simple and convenient to operate, and is only driven by a direct current signal with extremely low power consumption. However, the frequency of the comb teeth is limited by the microwave resonant cavity, and the frequency adjustable range of the microwave source is limited, and a conventional constant voltage source cannot realize the control with a quantum flux (h / 2e, about 2.07x10 -15 Wb) precision. SUMMARY

[0004] Therefore, in order to solve the problem of limited frequency adjustable range of the microwave source, the present application provides a microwave quantum frequency comb system, which can realize a microwave signal with a comb-shaped frequency distribution containing multiple frequency components, and the frequency of each component can be changed by real-time control and switching of the corresponding Josephson junction array lead through an external circuit program.

[0005] The present application provides a microwave quantum frequency comb system, which comprises at least three Josephson junction arrays. The first end of the first Josephson junction array is a high-frequency input end, and a microwave or high-speed pulse signal is input. The second end is connected to a terminal resistor. A plurality of direct current output end leads are arranged between the Josephson junctions of the first Josephson junction array. When two direct current output end leads are selected as direct current output ends, the number of Josephson junctions included between the selected direct current output ends is also different.

[0006] The two ends of the second to Nth Josephson junction arrays are high-frequency output terminals. Several DC input terminals are set between the Josephson junctions of the second to Nth Josephson junction arrays. When two DC input terminals are selected as input terminals, the number of Josephson junctions between the selected input terminals is also different.

[0007] The two DC output terminals of the first Josephson junction array are connected to the two DC input terminals of the second to Nth Josephson junction arrays through two filter modules respectively. The first Josephson junction array outputs voltage signals to the second to Nth Josephson junction arrays.

[0008] Thus, the second to Nth Josephson junction arrays output frequency-converted microwave signals at both ends;

[0009] It also includes a combiner, which selectively connects any two or more of the second to Nth Josephson junction arrays to combine the microwave signals output from both ends of the connected Josephson junction arrays.

[0010] Optionally, the number of Josephson nodes in the second to Nth Josephson node arrays can be different.

[0011] Optionally, the high-frequency input of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; a first filter module, the first end of which is connected to the DC output of the first Josephson junction array, and the second end of which is connected to the DC input of the second to Nth Josephson junction arrays respectively; a second filter module, the first end of which is connected to the DC output of the first Josephson junction array, and the second end of which is connected to the DC input of the second to Nth Josephson junction arrays; the second end of the first filter module is a positive DC output; the second end of the second filter module is a negative DC output; the voltage between the positive and negative outputs is V. dc =M(h / 2e)f1, where, V dc Let e ​​be the voltage across the M Josephson junctions, e be the electron charge, and h be Planck's constant.

[0012] Optionally, the two ends of the second to Nth Josephson junction array are connected to high-frequency output terminals; the output microwave signal frequency f m = (M / N) m )f1.

[0013] Optionally, the combiner combines the microwave signals output from the selected Josephson junction array and outputs the microwave signal containing the selected combined m frequency components: f = M·f1·[(1 / N1) + (1 / N2) + ... + (1 / N...] mM is the number of junctions between the direct current output terminals of the first Josephson junction array, m is the number of selected and combined junction arrays in the second to Nth Josephson junction arrays, N1 to N m are the numbers of junctions of the selected and combined junction arrays in the second to Nth Josephson junction arrays.

[0014] Optionally, the second to Nth Josephson junction arrays are also respectively connected with a third filter module and a fourth filter module, and a direct current is input at the other end of the third filter module and the fourth filter module.

[0015] Optionally, the input end of the first Josephson junction array is a microwave with a frequency of f1, and the first Josephson junction array is also respectively connected with a fifth filter module and a sixth filter module, and a direct current is input at the other end of the fifth filter module and the sixth filter module.

[0016] Optionally, the Josephson junction comprises a superconductor layer, an insulator layer and a superconductor layer arranged in sequence.

[0017] Optionally, the Josephson junction comprises a superconductor layer, a non-superconducting metal layer and a superconductor layer arranged in sequence.

[0018] Optionally, the corresponding combiner and the second to Nth Josephson junction arrays are opened and closed by an external circuit program, the number of switched Josephson junction arrays is controlled in real time, and the frequency conversion ratio is adjusted.

[0019] The technical scheme adopted in the present application can realize precise frequency conversion of the quantum precision of the microwave signal. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the following will briefly introduce the drawings involved in the embodiments, which are part of the present application. It should be pointed out that the illustrative embodiments and their related descriptions are only used to explain the technical content of the present application, and do not constitute any improper limitation on the present application. In the drawings:

[0021] Figure 1 The present application is a microwave quantum frequency comb system schematic diagram. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the following will be further described in detail by combining the embodiments and the drawings. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0023] The serial numbers of components in this document, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any sequence or technical meaning. Unless otherwise specified, the "connection" and "coupling" in this application include direct and indirect connections (couplings). In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on this application.

[0024] In this application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0025] A microwave quantum frequency comb system of the application comprises at least three Josephson junction arrays, the first end of the first Josephson junction array is a high-frequency input end, and a microwave or high-speed pulse signal is input, the second end is connected to a terminal resistor, and a plurality of direct current output terminal leads are arranged between the Josephson junctions of the first Josephson junction array, when two direct current output terminal leads are selected as direct current output terminals, the number of Josephson junctions included between the selected direct current output terminals is also different;

[0026] The two ends of the second to Nth Josephson junction array are high-frequency output ends, a plurality of direct current input terminal leads are arranged between the Josephson junctions of the second to Nth Josephson junction array, when two direct current input terminal leads are selected as input terminals, the number of Josephson junctions included between the selected input terminals is also different;

[0027] The two direct current output terminals of the first Josephson junction array are connected to the two direct current input terminals of the second to Nth Josephson junction array through two filter modules, respectively, and the first Josephson junction array outputs a voltage signal to the second to Nth Josephson junction array;

[0028] Thus, the two ends of the second to Nth Josephson junction array output a frequency-converted microwave signal;

[0029] The combiner selectively connects any two or more of the second to the Nth Josephson junction array, and combines the microwave signals output from the connected Josephson junction arrays.

[0030] In an embodiment, the number of Josephson junctions in the second to the Nth Josephson junction array is different.

[0031] In an embodiment, the high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; the first filter module has a first end connected to the DC output end of the first Josephson junction array, and a second end connected to the DC input end of the second to the Nth Josephson junction array; the second filter module has a first end connected to the DC output end of the first Josephson junction array, and a second end connected to the DC input end of the second to the Nth Josephson junction array; the second end of the first filter module is a positive DC output end; the second end of the second filter module is a negative DC output end; the voltage between the positive output end and the negative output end is V dc =M(h / 2e)f1, where V dc is the voltage generated across the M Josephson junctions, e is the electron charge, and h is the Planck constant.

[0032] In an embodiment, the second to the Nth Josephson junction array has a high-frequency output end connected to both ends; the output microwave signal has a frequency f m =(M / N m )f1, where Figure 1 f2 or f3.

[0033] In an embodiment, the combiner combines the microwave signals output from the selected Josephson junction arrays to output a microwave signal containing m frequency components: f=M·f1·[(1 / N1)+(1 / N2)+…+(1 / N m )], where M is the number of junctions between the DC output ends of the first Josephson junction array, m is the number of selected and combined junction arrays in the second to the Nth Josephson junction array, N1 to N m are the number of junctions in the selected and combined junction arrays in the second to the Nth Josephson junction array.

[0034] In an embodiment, the DC input end of the second to the Nth Josephson junction array is further connected to a third filter module and a fourth filter module, respectively, and a DC current is input to the other end of the third filter module and the fourth filter module.

[0035] In an embodiment, the input end of the first Josephson junction array is a microwave with a frequency of f1, and the two ends of the first Josephson junction array are further connected with a fifth filter module and a sixth filter module, and a direct current is input at the other end of the fifth filter module and the sixth filter module. Since a first Josephson junction array with a string of M series Josephson junctions is used to input a microwave with a frequency of f1 or a pulse with a repetition frequency of f1, a voltage of V=M(h / 2e)f1 can be generated, and when a microwave is used, appropriate bias currents need to be input to the first Josephson junction array from port 1 and port 2, and when a pulse is used, no bias current is needed. dc

[0036] In an embodiment, the Josephson junction comprises a superconductor layer, an insulator layer, and a superconductor layer arranged in sequence.

[0037] In an embodiment, the Josephson junction comprises a superconductor layer, a non-superconducting metal layer, and a superconductor layer arranged in sequence.

[0038] In an embodiment, the corresponding combiner and the second to Nth Josephson junction arrays are opened and closed by an external circuit program, the number of switched Josephson junction arrays is controlled in real time, and the frequency conversion ratio is adjusted.

[0039] In the embodiment, each Josephson junction can be composed of two superconductors weakly connected to each other, and the weakly connected structure can be a thin insulating layer, forming a superconductor-insulator-superconductor structure (S-I-S structure).

[0040] The Josephson junction can also be composed of two superconductors weakly connected to each other, and the weakly connected structure can be a small piece of non-superconducting metal, forming an S-N-S structure. The Josephson junction can also be composed of two superconductors weakly connected to each other, and the weakly connected structure can be a narrow part of the superconductivity of the contact point, forming a simple S-s-S structure.

[0041] As shown in Figure 1 A microwave quantum frequency comb system of the present application comprises at least three Josephson junction arrays, and the first Josephson junction array is connected with the second Josephson junction array and the third Josephson junction array. Figure 1 In the embodiment shown, three are taken as an example, the first end of the first Josephson junction array 10 is a high-frequency input end, a microwave or a high-speed pulse signal is input, the second end is connected with a terminal resistance, and a plurality of direct current output end leads are arranged between the Josephson junctions of the first Josephson junction array. When two direct current output end leads are selected as direct current output ends, the number of Josephson junctions included between the selected direct current output ends is also different each time.

[0042] ​The two ends of the second Josephson junction array 20 to the third Josephson junction array 30 are high frequency output ends, and a plurality of direct current input lead wires are arranged between the Josephson junctions of the second to third Josephson junction arrays, and the number of the Josephson junctions included between the selected two direct current input lead wires as input ends is different each time.

[0043] The two direct current output ends of the first Josephson junction array are connected to the two direct current input ends of the second to third Josephson junction arrays through two filter modules respectively, and the first Josephson junction array outputs a voltage signal to the second to third Josephson junction arrays;

[0044] Thus, the two ends of the second to third Josephson junction arrays output the frequency-converted microwave signal;

[0045] Further comprising a combiner 40 connected to the output ends of the second to third Josephson junction arrays, and the microwave signals output from the two ends of the connected Josephson junction arrays are combined and output. In the embodiment, there is one combiner 40 at each of the two output ends.

[0046] According to the inverse effect of the AC Josephson effect, a constant voltage, called "Shapiro voltage step", is generated at the two ends of the Josephson junction using current bias and microwave radiation with a frequency of f, and the formula is V dc =(h / 2e)f. This effect is used to realize a voltage reference with quantum accuracy. Using a junction array with M series-connected Josephson junctions, a voltage with quantum accuracy of V dc =M(h / 2e)f1 is generated by inputting a frequency f1, and by loading this voltage to another junction array with N series-connected Josephson junctions, a microwave signal with quantum accuracy of frequency f2=(M / N)f1 is obtained. Macroscopically, the two series of junction arrays arranged in this way can realize quantum-accuracy precision frequency conversion of the microwave signal.

[0047] According to the inverse effect of the AC Josephson effect, a constant voltage, called "Shapiro voltage step", is generated at the two ends of the Josephson junction using current bias and microwave radiation with a frequency of f, and the formula is V dc =(h / 2e)f. This effect is used to realize a voltage reference with quantum accuracy. Using a junction array with M series-connected Josephson junctions, a voltage with quantum accuracy of V dc =M(h / 2e)f1 is generated by inputting a frequency f1, and by loading this voltage to another junction array with N series-connected Josephson junctions, a microwave signal with quantum accuracy of frequency f2=(M / N)f1 is obtained. Macroscopically, the two series of junction arrays arranged in this way can realize quantum-accuracy precision frequency conversion of the microwave signal.

[0048] In this embodiment, the number of Josephson junctions included in the DC input terminals of the second to third Josephson junction arrays are different. The second array includes N1 Josephson junctions, and the third array includes N2 Josephson junctions.

[0049] In this embodiment, the high-frequency input of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; such as Figure 1 As shown, in this embodiment, the DC output terminal of the first Josephson junction array and the DC input terminals of the second to Nth Josephson junction arrays are each connected to a first filter module for filtering. The other DC output terminal of the first Josephson junction array and the other DC input terminal of the second to Nth Josephson junction arrays are each connected to a second filter module. The second terminal of the first filter module is a positive DC output terminal; the second terminal of the second filter module is a negative DC output terminal; the voltage between the positive and negative output terminals is V. dc =M(h / 2e)f1, where, V dc Let e ​​be the voltage across the M Josephson junctions, e be the electron charge, and h be Planck's constant.

[0050] In this embodiment, the two ends of the second to third Josephson junction arrays are connected to high-frequency output terminals; the output microwave signal frequency f m = (M / N) m )f1.

[0051] In this embodiment, the combiner combines the microwave signals output from the selected Josephson junction array, and outputs a microwave signal containing the selected combined m frequency components: f = M·f1·[(1 / N1)+(1 / N2)+…+(1 / N…] m M is the number of junctions between the DC output terminals of the first Josephson junction array, m is the number of junction arrays selected to be merged in the second to third Josephson junction arrays, in this embodiment m=2, N1 and N2 are the number of junction arrays selected to be merged in the second to third Josephson junction arrays.

[0052] In this embodiment, the DC input terminals of the second to third Josephson junction arrays are also connected to the third filter module 13 and the fourth filter module 14, respectively, and DC current is input at the other end ports 3 and 4 of the third filter module 13 and the fourth filter module 14.

[0053] In the embodiment, the input end of the first Josephson junction array is connected with a microwave with a frequency of f1, and the two ends of the first Josephson junction array are further connected with a fifth filter module 15 and a sixth filter module 16 respectively, and a direct current is input to the other ends of the fifth filter module 15 and the sixth filter module 16. When the microwave is used, the first Josephson junction array needs to be input with a suitable bias current from the port 1 and the port 2, and when the pulse is used, the first Josephson junction array does not need to be input with the bias current.

[0054] In the embodiment, a low-pass filter can also be arranged at each direct current output lead end of the first Josephson junction array, and a low-pass filter can also be arranged at each direct current input lead end of the second Josephson junction array.

[0055] In the embodiment, the Josephson junction comprises a superconductor layer, an insulator layer and a superconductor layer arranged in sequence.

[0056] In the embodiment, the Josephson junction comprises a superconductor layer, a non-superconductor metal layer and a superconductor layer arranged in sequence.

[0057] In the embodiment, the corresponding combiner and the second to third Josephson junction arrays are opened and closed by an external circuit program, the number of the switched Josephson junction arrays is controlled in real time, and the frequency conversion ratio is adjusted.

[0058] The embodiments of the application are described above in combination with the drawings, but the application is not limited to these specific embodiments. The above embodiments are only illustrative and non-restrictive. For those skilled in the art, under the guidance of the application, various forms of changes can be made without departing from the purpose of the application and the protection scope of the claims, and these changes should be considered as the protection scope of the application.

Claims

1. A microwave quantum frequency comb system, characterized by: The Josephson junction array includes at least three Josephson junction arrays, wherein the first end of the first Josephson junction array is a high-frequency input end, an input microwave or high-speed pulse signal is input, the second end is connected to a terminal resistance, and a plurality of direct-current output lead wires are arranged between the Josephson junctions of the first Josephson junction array; when two direct-current output lead wires are selected as direct-current output ends, the number of Josephson junctions included between the selected direct-current output ends is also different; The two ends of the second to Nth Josephson junction arrays are high-frequency output ends, a plurality of direct-current input lead wires are arranged between the Josephson junctions of the second to Nth Josephson junction arrays, and when two direct-current input lead wires are selected as input ends, the number of Josephson junctions included between the selected input ends is also different; The two direct-current output ends of the first Josephson junction array are connected to the two direct-current input ends of the second to Nth Josephson junction arrays through two filter modules, and the first Josephson junction array outputs a voltage signal to the second to Nth Josephson junction arrays; Thus, the two ends of the second to Nth Josephson junction arrays output a frequency-converted microwave signal; The combiner selectively connects at least two of the second to Nth Josephson junction arrays and combines and outputs the microwave signals output from the two ends of the connected Josephson junction arrays.

2. The microwave quantum frequency comb system of claim 1, wherein, The number of Josephson junctions included in the second to Nth Josephson junction arrays is different.

3. The microwave quantum frequency comb system of claim 2, wherein, The high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; the first filter module has a first end connected to a direct-current output end in the first Josephson junction array and a second end respectively connected to a direct-current input end in the second to Nth Josephson junction arrays; The second filter module has a first end connected to a direct-current output end in the first Josephson junction array and a second end connected to a direct-current input end in the second to Nth Josephson junction arrays; the second end of the first filter module is a positive direct-current output end; the second end of the second filter module is a negative direct-current output end; and the voltage between the positive direct-current output end and the negative direct-current output end is Vdc=M(h / 2e)f1, where M is the number of junctions between the direct-current output ends of the first Josephson junction array, e is the electronic charge, and h is the Planck constant.

4. The microwave quantum frequency comb system of claim 3, wherein, The two ends of the second to Nth Josephson junction arrays are connected to high-frequency output ends; and the output microwave signal has a frequency of fm=(M / Nm)f1, where M is the number of junctions between the direct-current output ends of the first Josephson junction array, and Nm is the number of junctions in the selected combined junction array of the Nth Josephson junction array.

5. The microwave quantum frequency comb system of claim 3, wherein, The microwave signals output by the selected Josephson junction arrays are combined by the combiner to output a microwave signal containing m frequency components selected for combination: f=M·f1·[(1 / N1)+(1 / N2)+…+(1 / Nm)], where M is the number of junctions between the direct-current output ends of the first Josephson junction array, m is the number of selected combined junction arrays in the second to Nth Josephson junction arrays, and N1 to Nm are the numbers of junctions in the selected combined junction arrays of the second to Nth Josephson junction arrays.

6. The microwave quantum frequency comb system of claim 3, wherein, The direct current input end of the second to Nth Josephson junction array is also connected with a third filter module and a fourth filter module, and direct current is input at the other end of the third filter module and the fourth filter module.

7. The microwave quantum frequency comb system of claim 3, wherein, The input end of the first Josephson junction array is a microwave with a frequency of f1, and the direct current output end of the first Josephson junction array is also connected with a fifth filter module and a sixth filter module, and direct current is input at the other end of the fifth filter module and the sixth filter module.

8. The microwave quantum frequency comb system of claim 1, wherein, The Josephson junction comprises a superconductor layer, an insulator layer and a superconductor layer arranged in sequence.

9. The microwave quantum frequency comb system of claim 1, wherein, The Josephson junction comprises a superconductor layer, a non-superconducting metal layer and a superconductor layer arranged in sequence.

10. The microwave quantum frequency comb system of claim 1, wherein, The corresponding combiner and the second to Nth Josephson junction array are opened and closed by an external circuit program, the number of the Josephson junction arrays is controlled in real time, and the frequency conversion ratio is adjusted.

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